# std::less<void>

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< cpp‎ | utility‎ | functional

Defined in header `<functional>` |  |
template<> class less<void>; |  | (since C++14)

std::less<void> is a specialization of std::less with parameter and return type deduced.

### Nested types

Nested type | Definition
`is_transparent` | unspecified

### Member functions

operator() | tests if lhs compares less than rhs (public member function)

## std::less<void>::operator()

template< class T, class U > constexpr auto operator()( T&& lhs, U&& rhs ) const -> decltype(std::forward<T>(lhs) < std::forward<U>(rhs)); |  |

Returns the result of std::forward<T>(lhs) < std::forward<U>(rhs).

### Parameters

lhs, rhs | - | values to compare

### Return value

std::forward<T>(lhs) < std::forward<U>(rhs).

If a built-in operator comparing pointers is called, the result is consistent with the implementation-defined strict total order over pointers.

### Exceptions

May throw implementation-defined exceptions.

### Example

Run this code

    #include <algorithm>
    #include <functional>

    constexpr bool strictly_negative(int lhs)
    {
        return std::less<>()(lhs, 0);
    }

    int main()
    {
        constexpr signed low = 010;
        constexpr unsigned high = 10;
        std::less<> less{};
        static_assert(less(low, high));

        constexpr static auto arr = {0, -1, -2, -3, -4, -5};
        static_assert(!std::all_of(arr.begin(), arr.end(), strictly_negative));
        static_assert(std::all_of(arr.begin() + 1, arr.end(), strictly_negative));
    }

### Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR | Applied to | Behavior as published | Correct behavior
--- | --- | --- | ---
LWG 2562 | C++98 | the pointer total order might be inconsistent | guaranteed to be consistent

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